Brain distribution and bioavailability of elacridar after different routes of administration in the mouse

Discovery of BI-9508, a Brain-Penetrant GPR88-Receptor-Agonist Tool Compound for In Vivo Mouse Studies

Decreased activity and expression of the G-protein coupled receptor GPR88 is linked to many behavior-linked neurological disorders. Published preclinical GPR88 allosteric agonists all have in vivo pharmacokinetic properties that preclude their progression to the clinic, including high lipophilicity and poor brain penetration. Here, we describe our attempts to improve GPR88 agonists' drug-like properties and our analysis of the trade-offs required to successfully target GPR88's allosteric pocket. We discovered two new GPR88 agonists: One that reduced morphine-induced locomotor activity in a murine proof-of-concept study, and the atropoisomeric BI-9508, which is a brain penetrant and has improved pharmacokinetic properties and dosing that recommend it for future in vivo studies in rodents. BI-9508 still suffers from high lipophilicity, and research on this series was halted. Because of its utility as a tool compound, we now offer researchers access to BI-9508 and a negative control free of charge via Boehringer Ingelheim's open innovation portal opnMe.com.

Cancer sensitizing effect of deazaflavin analogs is associated with increased intracellular drug accumulation

As part of our efforts geared towards developing mechanism-based cancer sensitizing agents, we have previously synthesized and characterized novel deazaflavin analogs as potent tyrosyl DNA phosphodiesterase 2 (TDP2) inhibitors for combination treatments with topoisomerase II (TOP2) poisons. Interestingly, the sensitizing effect of a few analogs toward TOP2 poison etoposide (ETP) was associated with a significant increase in intracellular drug accumulation, which could be an alternative mechanism to boost the clinical efficacy of ETP in cancer chemotherapies. Hence, we evaluated more deazaflavin TDP2 inhibitors for their impact on drug retention in cancer cells. We found that all but one tested TDP2 inhibitors substantially increased the ETP retention in DT40 cells. Particularly, we identified an exceptionally potent analog, ZW-1226, which at 3 nM increased the intracellular ETP by 13-fold. Significantly, ZW-1226 also stimulated cellular accumulation of two other anticancer drugs, TOP2 poison teniposide and antifolate pemetrexed, and produced an effect more pronounced than those of ABC transporter inhibitors verapamil and elacridar in human leukemic CCRF-CEM cells toward ETP. Lastly, ZW-1226 potentiated the action of ETP in the sensitive human CCRF-CEM cells and a few resistant non-small-cell lung cancer (NSCLC) cells, including H460 and H838 cells. Collectively, the results of this study strongly suggest that deazaflavin analog ZW-1226 could be an effective cancer sensitizing agent which warrants further investigation.

ABCB1 and ABCG2 Regulation at the Blood-Brain Barrier: Potential New Targets to Improve Brain Drug Delivery

The drug efflux transporters ABCB1 and ABCG2 at the blood-brain barrier limit the delivery of drugs into the brain. Strategies to overcome ABCB1/ABCG2 have been largely unsuccessful, which poses a tremendous clinical problem to successfully treat central nervous system (CNS) diseases. Understanding basic transporter biology, including intracellular regulation mechanisms that control these transporters, is critical to solving this clinical problem.In this comprehensive review, we summarize current knowledge on signaling pathways that regulate ABCB1/ABCG2 at the blood-brain barrier. In Section I, we give a historical overview on blood-brain barrier research and introduce the role that ABCB1 and ABCG2 play in this context. In Section II, we summarize the most important strategies that have been tested to overcome the ABCB1/ABCG2 efflux system at the blood-brain barrier. In Section III, the main component of this review, we provide detailed information on the signaling pathways that have been identified to control ABCB1/ABCG2 at the blood-brain barrier and their potential clinical relevance. This is followed by Section IV, where we explain the clinical implications of ABCB1/ABCG2 regulation in the context of CNS disease. Lastly, in Section V, we conclude by highlighting examples of how transporter regulation could be targeted for therapeutic purposes in the clinic. SIGNIFICANCE STATEMENT: The ABCB1/ABCG2 drug efflux system at the blood-brain barrier poses a significant problem to successful drug delivery to the brain. The article reviews signaling pathways that regulate blood-brain barrier ABCB1/ABCG2 and could potentially be targeted for therapeutic purposes.

Bench-to-bedside investigations of H3 K27-altered diffuse midline glioma: drug targets and potential pharmacotherapies

INTRODUCTION

H3 K27-altered diffuse midline glioma (DMG) is the most common malignant brainstem tumor in the pediatric population. Despite enormous preclinical and clinical efforts, the prognosis remains dismal, with fewer than 10% of patients surviving for two years after diagnosis. Fractionated radiation remains the only standard treatment options for DMG. Developing novel treatments and therapeutic delivery methods is critical to improving outcomes in this devastating disease.

AREAS COVERED

This review addresses recent advances in molecularly targeted pharmacotherapy and immunotherapy in DMG. The clinical presentation, diagnostic workup, unique pathological challenges, and current clinical trials are highlighted throughout.

EXPERT OPINION

Promising pharmacotherapies targeting various components of DMG pathology and the application of immunotherapies have the potential to improve patient outcomes. However, novel approaches are needed to truly revolutionize treatment for this tumor. First, combinational therapy should be employed, as DMG can develop resistance to single-agent approaches and many therapies are susceptible to rapid clearance from the brain. Second, drug-tumor residence time, i.e. the time for which a therapeutic is present at efficacious concentrations within the tumor, must be maximized to facilitate a durable treatment response. Engineering extended drug delivery methods with minimal off-tumor toxicity should be a focus of future studies.

Syntheses and evaluation of acridone derivatives as anticancer agents targeting Kras promoter i-motif structure

Two series of novel acridone derivatives were designed and synthesized, with their anticancer activity evaluated. Most of these compounds showed potent antiproliferative activity against cancer cell lines. Among them, compound C4 with dual 1,2,3-triazol moieties exhibited the most potent activity against Hep-G2 cells with IC₅₀ value determined to be 6.29 ± 0.93 μM. Subsequent experiments showed that C4 could bind to and destabilize Kras gene promoter i-motif structure without significant interaction with its corresponding G-quadruplex. C4 could down-regulate Kras expression in Hep-G2 cells, possibly due to its interaction with the Kras i-motif. Further cellular studies indicated that C4 could induce apoptosis of Hep-G2 cells, possibly related to its effect on mitochondrial dysfunction. These results indicated that C4 could be further developed as a promising anticancer agent.

Central Nervous System Distribution of the Ataxia-Telangiectasia Mutated Kinase Inhibitor AZD1390: Implications for the Treatment of Brain Tumors

Effective drug delivery to the brain is critical for the treatment of glioblastoma (GBM), an aggressive and invasive primary brain tumor that has a dismal prognosis. Radiation therapy, the mainstay of brain tumor treatment, works by inducing DNA damage. Therefore, inhibiting DNA damage response (DDR) pathways can sensitize tumor cells to radiation and enhance cytotoxicity. AZD1390 is an inhibitor of ataxia-telangiectasia mutated kinase, a critical regulator of DDR. Our in vivo studies in the mouse indicate that delivery of AZD1390 to the central nervous system (CNS) is restricted due to active efflux by P-glycoprotein (P-gp). The free fraction of AZD1390 in brain and spinal cord were found to be low, thereby reducing the partitioning of free drug to these organs. Coadministration of an efflux inhibitor significantly increased CNS exposure of AZD1390. No differences were observed in distribution of AZD1390 within different anatomic regions of CNS, and the functional activity of P-gp and breast cancer resistance protein also remained the same across brain regions. In an intracranial GBM patient-derived xenograft model, AZD1390 accumulation was higher in the tumor core and rim compared with surrounding brain. Despite this heterogenous delivery within tumor-bearing brain, AZD1390 concentrations in normal brain, tumor rim, and tumor core were above in vitro effective radiosensitizing concentrations. These results indicate that despite being a substrate of efflux in the mouse brain, sufficient AZD1390 exposure is anticipated even in regions of normal brain. SIGNIFICANCE STATEMENT: Given the invasive nature of glioblastoma (GBM), tumor cells are often protected by an intact blood-brain barrier, requiring the development of brain-penetrant molecules for effective treatment. We show that efflux mediated by P-glycoprotein (P-gp) limits central nervous system (CNS) distribution of AZD1390 and that there are no distributional differences within anatomical regions of CNS. Despite efflux by P-gp, concentrations effective for potent radiosensitization are achieved in GBM tumor-bearing mouse brains, indicating that AZD1390 is an attractive molecule for clinical development of brain tumors.

Target-Agnostic P-Glycoprotein Assessment Yields Strategies to Evade Efflux, Leading to a BRAF Inhibitor with Intracranial Efficacy

The blood-brain barrier (BBB) presents a major hurdle in the development of central nervous system (CNS) active therapeutics, and expression of the P-glycoprotein (P-gp) efflux transporter at the blood-brain interface further impedes BBB penetrance of most small molecules. Designing efflux liabilities out of compounds can be laborious, and there is currently no generalizable approach to directly transform periphery-limited agents to ones active in the CNS. Here, we describe a target-agnostic, prospective assessment of P-gp efflux using diverse compounds. Our results demonstrate that reducing the molecular size or appending a carboxylic acid in many cases enables evasion of P-gp efflux in cell-based experiments and in mice. These strategies were then applied to transform a periphery-limited ^V600EBRAF inhibitor, dabrafenib, into versions that possess potent and selective anti-cancer activity but now also evade P-gp-mediated efflux. When compared to dabrafenib, the compound developed herein (everafenib) has superior BBB penetrance and superior efficacy in an intracranial mouse model of metastatic melanoma, suggesting it as a lead candidate for the treatment of melanoma metastases to the brain and gliomas with BRAF mutation. More generally, the results described herein suggest the actionability of the trends observed in these target-agnostic efflux studies and provide guidance for the conversion of non-BBB-penetrant drugs into versions that are BBB-penetrant and efficacious.

Rifampin and ritonavir increase oral availability and elacridar enhances overall exposure and brain accumulation of the NTRK inhibitor larotrectinib

INTRODUCTION

Larotrectinib is an FDA-approved oral small-molecule inhibitor for neurotrophic tropomyosin receptor kinase (NTRK) fusion-positive cancer treatment. Here larotrectinib pharmacokinetic behavior upon co-administration with prototypical inhibitors of the efflux transporters ABCB1/ABCG2 (elacridar), the SLCO1A/1B (OATP1A/1B) uptake transporters (rifampin), and the drug-metabolizing enzyme CYP3A (ritonavir), respectively, was investigated.

METHODS

Inhibitors were orally administered prior to oral larotrectinib (10 mg/kg) to relevant genetically modified mouse models. Larotrectinib plasma and tissue homogenate concentrations were measured by a liquid chromatography-tandem mass spectrometric assay.

RESULTS

Elacridar increased oral availability (2.7-fold) and markedly improved brain-to-plasma ratios (5.0-fold) of larotrectinib in wild-type mice. Mouse (m)Oatp1a/1b but not hepatic transgenic human (h)OATP1B1 or -1B3 restricted larotrectinib oral availability and affected its tissue distribution. Rifampin enhanced larotrectinib oral availability not only in wild-type mice (1.9-fold), but surprisingly also in Slco1a/1b^-/- mice (1.7-fold). Similarly, ritonavir increased the larotrectinib plasma exposure in both wild-type (1.5-fold) and Cyp3a^-/- mice (1.7-fold). Intriguingly, both rifampin and ritonavir decreased liver and/or intestinal larotrectinib levels in all related experimental groups, suggesting additional inhibition of enterohepatic Abcb1a/1b activity.

CONCLUSIONS

Elacridar enhances both larotrectinib plasma and tissue exposure and especially relative brain penetration, which might be therapeutically relevant. Hepatic mOatp1a/1b but not hOATP1B1 or -1B3 transported larotrectinib. Additionally, rifampin enhances larotrectinib systemic exposure, most likely by inhibiting mOatp1a/1b, but probably also hepatic and/or intestinal mAbcb1. Similar to rifampin, dual-inhibition functions of ritonavir affecting both CYP3A enzymes and enterohepatic Abcb1 transporters enhanced larotrectinib oral availability. The obtained insights may be used to further optimize the clinical-therapeutic application of larotrectinib.

Brain Distribution of Berzosertib: An Ataxia Telangiectasia and Rad3-Related Protein Inhibitor for the Treatment of Glioblastoma

The effective treatment of brain tumors is a considerable challenge in part because of the presence of the blood-brain barrier (BBB) that limits drug delivery. Glioblastoma multiforme (GBM) is an aggressive and infiltrative primary brain tumor with an extremely poor prognosis after standard-of-care therapy with surgery, radiotherapy (RT), and chemotherapy. DNA damage response (DDR) pathways play a critical role in DNA repair in cancer cells, and inhibition of these pathways can potentially augment RT and chemotherapy tumor cell toxicity. The ataxia telangiectasia and Rad3-related protein (ATR) kinase is a key regulator of the DDR network and is potently and selectively inhibited by the ATR inhibitor berzosertib. Although in vitro studies demonstrate a synergistic effect of berzosertib in combination with temozolomide, in vivo efficacy studies have yet to recapitulate this observation using intracranial tumor models. In the current study, we demonstrate that delivery of berzosertib to the brain is restricted by efflux at the BBB. Berzosertib has a high binding affinity to brain tissue compared with plasma, thereby leading to low free drug concentrations in the brain. Berzosertib distribution is heterogenous within the tumor, wherein concentrations are substantially lower in normal brain and invasive tumor rim (wherein the BBB is intact) when compared with those in the tumor core (wherein the BBB is leaky). These results demonstrate that high tissue binding and limited and heterogenous brain distribution of berzosertib may be important factors that influence the efficacy of berzosertib therapy in GBM. SIGNIFICANCE STATEMENT: This study examined the brain delivery and efficacy of berzosertib in patient-derived xenograft models of glioblastoma multiforme (GBM). Berzosertib is actively effluxed at the blood-brain barrier and is highly bound to brain tissue, leading to low free drug concentrations in the brain. Berzosertib is heterogeneously distributed into different regions of the brain and tumor and, in this study, was not efficacious in vivo when combined with temozolomide. These factors inform the future clinical utility of berzosertib for GBM.

Synthesis, and antimalarial and antibacterial activities of marine alkaloids

The activities of marine alkaloids are manifested in antifungus and antimalaria. The optimization process, chemical synthesis, antimalarial activity, and antibacterial activity of various compounds were discussed.

Discovery of new pyrimidopyrrolizine/indolizine-based derivatives as P-glycoprotein inhibitors: Design, synthesis, cytotoxicity, and MDR reversal activities

Targeting P-glycoprotein (P-gp, ABCB1 transporter), which plays an essential role in multi-drug resistance (MDR) in cancers, with new cytotoxic agents is a promising strategy in cancer chemotherapy. In the current study, we report the synthesis of thirteen novel pyrimidopyrrolizine, pyrimidoindolizine, and diazepinopyrrolizine derivatives. The new compounds exhibited cytotoxic activities against MCF7, A2780 and HT29 cancer cell lines (IC₅₀ = 0.02-19.58 μM) and MRC5 (IC₅₀ = 0.17-20.57 μM). The six most active compounds (23b, 24a,b and, 31c-e) were evaluated for their MDR reversal activities in MCF7/ADR cells. Mechanistic study using real-time PCR revealed the ability of compound 31c to inhibit P-gp. In addition, compound 31c increased the accumulation of Rho123 inside MCF7/ADR cells in a dose-dependent manner compared to verapamil. Compound 31c arrested the cell cycle of MCF7 cells at the G₁ phase. Compound 31c also caused a significant dose-dependent increase of early and late apoptotic events. Molecular docking analysis revealed a high binding affinity for compound 31c toward P-gp. Like zosuquidar, compound 31c displayed one hydrogen bond and several hydrophobic interactions with amino acids in P-gp. These results indicated that compound 31c represents a potential anticancer candidate with MDR reversal activity.

Optimization of dose and route of administration of the P-glycoprotein inhibitor, valspodar (PSC-833) and the P-glycoprotein and breast cancer resistance protein dual-inhibitor, elacridar (GF120918) as dual infusion in rats

Transporters can play a key role in the absorption, distribution, metabolism, and excretion of drugs. Understanding these contributions early in drug discovery allows for more accurate projection of the clinical pharmacokinetics. One method to assess the impact of transporters in vivo involves co‐dosing specific inhibitors. The objective of the present study was to optimize the dose and route of administration of a P‐glycoprotein (P‐gp) inhibitor, valspodar (PSC833), and a dual P‐gp/breast cancer resistance protein (BCRP) inhibitor, elacridar (GF120918), by assessing the transporters’ impact on brain penetration and absorption. A dual‐infusion strategy was implemented to allow for flexibility with dose formulation. The chemical inhibitor was dosed intravenously via the femoral artery, and a cassette of known substrates was infused via the jugular vein. Valspodar or elacridar was administered as 4.5‐hour constant infusions over a range of doses. To assess the degree of inhibition, the resulting ratios of brain and plasma concentrations, Kp's, of the known substrates were compared to the vehicle control. These data demonstrated that doses greater than 0.9 mg/hr/kg valspodar and 8.9 mg/hr/kg elacridar were sufficient to inhibit P‐gp‐ and BCRP‐mediated efflux at the blood‐brain barrier in rats without any tolerability issues. Confirmation of BBB restriction by efflux transporters in preclinical species allows for subsequent prediction in humans based upon the proteomic expression at rodent and human BBB. Overall, the approach can also be applied to inhibition of efflux at other tissues (gut absorption, liver clearance) or can be extended to other transporters of interest using alternate inhibitors.

A combo-strategy to improve brain delivery of antiepileptic drugs: Focus on BCRP and intranasal administration

The breast cancer resistance protein (BCRP) is an efflux transporter expressed at the apical surface of human brain endothelial cells of the blood-brain barrier (BBB). It was proposed as one of the transporters responsible for the development of drug resistance to several central nervous system (CNS) drugs, including antiepileptic drugs (AEDs). In this context, the present work aimed to characterize the interaction between new-generation AEDs, lacosamide, levetiracetam and zonisamide, and BCRP, in order to investigate whether intranasal administration can successfully avoid the impact of BCRP on brain drug distribution, preventing the development of refractory epilepsy. Firstly, BCRP substrates and/or inhibitors were identified resorting to intracellular accumulation and bidirectional transport assays on Madin-Darby canine kidney (MDCK) cells and the transfected cell line with human ABCG2 (MDCK-BCRP). Furthermore, in vivo pharmacokinetic studies were carried out for BCRP substrates with and without elacridar, a well-known P-gp and BCRP modulator, to assess the impact of efflux inhibition on brain drug distribution. The extent of drug equilibration between plasma and brain was compared after intravenous (IV) and intranasal administration to mice. Among the three tested AEDs, zonisamide was the only AED identified as BCRP substrate in vitro, as demonstrated by the net flux ratio of 2.73, which decreased 53.85 % in the presence of a BCRP inhibitor, Ko143. Lacosamide revealed to inhibit BCRP in all tested concentrations (2.5-75 µM), exhibiting a significant increase (p < 0.001) of the intracellular accumulation of a BCRP substrate (Hoechst 33342) in MDCK-BCRP cells. Levetiracetam did not behave as a BCRP substrate nor inhibitor. After IV administration, the plasma concentrations of zonisamide were unaffected by elacridar, but its extent of brain exposure increased three-fold (as assessed by AUC_t, 674.12 vs 284.47 µg.min/mL). These results corroborate the previous in vitro findings, suggesting that BCRP is involved in the transport of zonisamide through the BBB. In opposition, no significant changes were found in plasma or brain concentrations after the administration of zonisamide by intranasal route, indicating that the influence of BCRP is less relevant than for IV route. In addition, direct nose-to-brain delivery of zonisamide, given by the direct transport percentage, was approximately 49 %. Altogether, these assays demonstrated that the impact of BCRP on the delivery of zonisamide to the brain is lower after intranasal administration, probably due to direct nose-to-brain transport. Therefore, the intranasal administration of AEDs may be a relevant strategy to avoid the impact of efflux transporters at the BBB and the development of drug resistance.

A Comprehensive Review on Source, Types, Effects, Nanotechnology, Detection, and Therapeutic Management of Reactive Carbonyl Species Associated with Various Chronic Diseases

Continuous oxidation of carbohydrates, lipids, and amino acids generate extremely reactive carbonyl species (RCS). Human body comprises some important RCS namely hexanal, acrolein, 4-hydroxy-2-nonenal, methylglyoxal, malondialdehyde, isolevuglandins, and 4-oxo-2- nonenal etc. These RCS damage important cellular components including proteins, nucleic acids, and lipids, which manifests cytotoxicity, mutagenicity, multitude of adducts and crosslinks that are connected to ageing and various chronic diseases like inflammatory disease, atherosclerosis, cerebral ischemia, diabetes, cancer, neurodegenerative diseases and cardiovascular disease. The constant prevalence of RCS in living cells suggests their importance in signal transduction and gene expression. Extensive knowledge of RCS properties, metabolism and relation with metabolic diseases would assist in development of effective approach to prevent numerous chronic diseases. Treatment approaches for RCS associated diseases involve endogenous RCS metabolizers, carbonyl metabolizing enzyme inducers, and RCS scavengers. Limited bioavailability and bio efficacy of RCS sequesters suggest importance of nanoparticles and nanocarriers. Identification of RCS and screening of compounds ability to sequester RCS employ several bioassays and analytical techniques. Present review describes in-depth study of RCS sources, types, properties, identification techniques, therapeutic approaches, nanocarriers, and their role in various diseases. This study will give an idea for therapeutic development to combat the RCS associated chronic diseases.

Theaflavin-Containing Black Tea Extract: A Potential DNA Methyltransferase Inhibitor in Human Colon Cancer Cells and Ehrlich Ascites Carcinoma-Induced Solid Tumors in Mice

Tea is the most popularly consumed beverage in the world. Theaflavin and thearubigins are the key bioactive compounds of black tea that have anticarcinogenic properties as reported in several studies. However, the epigenetic potential of these compounds has not yet been explored. DNA methyltransferase (DNMT) enzymes induce methylation of DNA at cytosine residues and play a significant role in epigenetic regulation and cancer therapy. The present study has explored the role of black tea as a DNMT inhibitor in the prevention of cancer. Herein, the effect of theaflavin has been studied in colon cancer cell line (HCT-116) and EAC-induced solid tumors in mice. It was found that theaflavin prevented cell proliferation and inhibited tumor progression as well. In silico study showed that theaflavin interacted with DNMT1 and DNMT3a enzymes and blocked their activity. Theaflavin also decreased DNMT activity In Vitro and In Vivo as evident from the DNMT activity assay. Results of immunohistochemistry revealed that theaflavin reduced DNMT expression in the tumors of mice. Taken together, our findings showed that theaflavin has a potential role as a DNMT inhibitor in HCT-116 cell line and EAC induced solid tumors in mice.

Retracted Article: The synthesis and biological activity of marine alkaloid derivatives and analogues

The ocean is the origin of life, with a unique ecological environment, which has given birth to a wealth of marine organisms. The ocean is an important source of biological resources and tens of thousands of monomeric compounds have been separated from marine organisms using modern separation technology. Most of these monomeric compounds have some kind of biological activity that has attracted extensive attention from researchers. Marine alkaloids are a kind of compound that can be separated from marine organisms. They have complex and special chemical structures, but at the same time, they can show diversity in biological activities. The biological activities of marine alkaloids mainly manifest in the form of anti-tumor, anti-fungus, anti-viral, anti-malaria, and anti-osteoporosis properties. Many marine alkaloids have good medicinal prospects and can possibly be used as anti-tumor, anti-viral, and anti-fungal clinical drugs or as lead compounds. The limited amounts of marine alkaloids that can be obtained by separation, coupled with the high cytotoxicity and low selectivity of these lead compounds, has restricted the clinical research and industrial development of marine alkaloids. Marine alkaloid derivatives and analogues have been obtained via rational drug design and chemical synthesis, to make up for the shortcomings of marine alkaloids; this has become an urgent subject for research and development. This work systematically reviews the recent developments relating to marine alkaloid derivatives and analogues in the field of medical chemistry over the last 10 years (2010-2019). We divide marine alkaloid derivatives and analogues into five types from the point-of-view of biological activity and elaborated on these activities. We also briefly discuss the optimization process, chemical synthesis, biological activity evaluation, and structure-activity relationship (SAR) of each of these compounds. The abundant SAR data provides reasonable approaches for the design and development of new biologically active marine alkaloid derivatives and analogues.

Profiling and Identification of Omeprazole Metabolites in Mouse Brain and Plasma by Isotope Ratio-Monitoring Liquid Chromatography-Mass Spectrometric Method

Neuro–inflammation is known to be one of the pathogenesis for the degenerative central nervous system (CNS) disease. Recently various approaches for the treatment of brain diseases by controlling neuro-inflammation in the brain have been introduced. In this respect, there is a continuous demand for CNS drugs, which could be safer and more effective. Omeprazole, a well-known proton-pump inhibitor (PPI) is generally prescribed for the treatment of peptic ulcer. In addition to the anti-gastric acid secretion mechanism, recent studies showed that omeprazole or PPIs would likely have anti-inflammation effects in vitro and in vivo, but their effects on anti-inflammation in brain are still unknown. In this study, omeprazole and its metabolites in a mouse’s brain after various routes of administration have been explored by stable isotope ratio-patterning liquid chromatography–mass spectrometric method. First, a simple liquid chromatography–mass spectrometric (LC–MS) method was established for the quantification of omeprazole in mouse plasma and brain. After that, omeprazole and its stable isotope (D3–omeprazole) were concomitantly administered through various routes to mice in order to identify novel metabolites characteristically observed in the mouse brain and were analyzed using a different LC–MS method with information-dependent analysis (IDA) scan. With this unique approach, several new metabolites of omeprazole were identified by the mass difference between omeprazole and stable isotope in both brain and plasma samples. A total of seventeen metabolites were observed, and the observed metabolites were different from each administration route or each matrix (brain or plasma). The brain pharmacokinetic profiles and brain-to-plasma partition coefficient (Kp) were also evaluated in a satellite study. Overall, these results provide better insights to understand the CNS-related biological effects of omeprazole and its metabolites in vivo.

Intraperitoneal Route of Drug Administration: Should it Be Used in Experimental Animal Studies?

Intraperitoneal (IP) route of drug administration in laboratory animals is a common practice in many in vivo studies of disease models. While this route is an easy to master, quick, suitable for chronic treatments and with low impact of stress on laboratory rodents, there is a common concern that it may not be an acceptable route for drug administration in experimental studies. The latter is likely due to sparsity of information regarding pharmacokinetics of pharmacological agents and the mechanisms through which agents get systemic exposure after IP administration. In this review, we summarize the main mechanisms involved in bioavailability of IP administered drugs and provide examples of pharmacokinetic profiles for small and large molecules in comparison to other routes of administration. We conclude with a notion that IP administration of drugs in experimental studies involving rodents is a justifiable route for pharmacological and proof-of-concept studies where the goal is to evaluate the effect(s) of target engagement rather than properties of a drug formulation and/or its pharmacokinetics for clinical translation.

Physical blood-brain barrier disruption induced by focused ultrasound does not overcome the transporter-mediated efflux of erlotinib

Overcoming the efflux mediated by ATP-binding cassette (ABC) transporters at the blood-brain barrier (BBB) remains a challenge for the delivery of small molecule tyrosine kinase inhibitors (TKIs) such as erlotinib to the brain. Inhibition of ABCB1 and ABCG2 at the mouse BBB improved the BBB permeation of erlotinib but could not be achieved in humans. BBB disruption induced by focused ultrasound (FUS) was investigated as a strategy to overcome the efflux transport of erlotinib in vivo. In rats, FUS combined with microbubbles allowed for a large and spatially controlled disruption of the BBB in the left hemisphere. ABCB1/ABCG2 inhibition was performed using elacridar (10 mg/kg i.v). The brain kinetics of erlotinib was studied using ¹¹C-erlotinib Positron Emission Tomography (PET) imaging in 5 groups (n = 4-5 rats per group) including a baseline group, immediately after sonication (FUS), 48 h after FUS (FUS + 48 h), elacridar (ELA) and their combination (FUS + ELA). BBB integrity was assessed using the Evan's Blue (EB) extravasation test. Brain exposure to ¹¹C-erlotinib was measured as the area under the curve (AUC) of the brain kinetics (% injected dose (%ID) versus time (min)) in volumes corresponding to the disrupted (left) and the intact (right) hemispheres, respectively. EB extravasation highlighted BBB disruption in the left hemisphere of animals of the FUS and FUS + ELA groups but not in the control and ELA groups. EB extravasation was not observed 48 h after FUS suggesting recovery of BBB integrity. Compared with the control group (AUC_Baseline = 1.4 ± 0.5%ID.min), physical BBB disruption did not impact the brain kinetics of ¹¹C-erlotinib in the left hemisphere (p > .05) either immediately (AUC_FUS = 1.2 ± 0.1%ID.min) or 48 h after FUS (AUC_FUS+48h = 1.1 ± 0.3%ID.min). Elacridar similarly increased ¹¹C-erlotinib brain exposure to the left hemisphere in the absence (AUC_ELA = 2.2 ± 0.5%ID.min, p < .001) and in the presence of BBB disruption (AUC_FUS+ELA = 2.1 ± 0.5%ID.min, p < .001). AUC_left was never significantly different from AUC_right (p > .05), in any of the tested conditions. BBB integrity is not the rate limiting step for erlotinib delivery to the brain which is mainly governed by ABC-mediated efflux. Efflux transport of erlotinib persisted despite BBB disruption.

Intravenous infusion for the controlled exposure to the dual ABCB1 and ABCG2 inhibitor elacridar in nonhuman primates

Elacridar (GF120918) is a highly potent inhibitor of both P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2), the main efflux transporters expressed at the blood-brain barrier (BBB). Elacridar shows very low aqueous solubility, which complicates its formulation for i.v. administration. An intravenous infusion protocol would be preferred to achieve high and controlled plasma concentrations of elacridar in large animals, including nonhuman primates. Formulation of elacridar for i.v. infusion was achieved using a co-solvent strategy, resulting in an aqueous dispersion with a final concentration of 5 g L^-1 elacridar with tetrahydrofuran (5% w/v) in aqueous D-glucose solution (2.5%, w/v). Particle size (mean = 2.8 ± 0.9 μm) remained stable for 150 min. The preparation was i.v. administered as a continuous infusion (12 mg kg^-1 h^-1 for 90 min) to three baboons. Arterial and venous plasma pharmacokinetics (PK) of elacridar were monitored using a newly developed and validated HPLC-UV method. Elacridar concentration increased rapidly to reach a plateau at 9.5 μg mL^-1 within 20 min after the start of infusion. Elacridar PK in venous plasma did not differ from arterial plasma facing the BBB, indicating the absence of an arteriovenous concentration gradient. Intravenous infusion of elacridar allows for controlled exposure of the BBB and offers a useful tool to assess the impact of ABCB1/ABCG2 on drug disposition to the brain in nonhuman primates, a relevant animal model for the study of transporter function at the BBB.

Pheophorbide A: Fluorescent Bcrp Substrate to Measure Oral Drug-Drug Interactions in Real-Time In Vivo

We investigated whether pheophorbide A (PhA) could serve as a selective breast cancer resistance protein (BCRP) substrate (victim) to screen in vivo using fluorescent live animal imaging for transporter-mediated interactions with orally administered inhibitors (perpetrators), and whether that could be coupled with serum sampling to measure the systemic concentration of PhA with a fast-throughput in vitro fluorescent assay. PhA is a breakdown product of chlorophyll and is highly fluorescent in the near-infrared (NIR) spectrum. Whole-body NIR fluorescence was greater in the Bcrp KO compared with wild-type (WT) mice fed a regular diet containing chlorophyll and PhA, with fluorescence in WT mice confined to the intestine. PhA intestinal enterocyte fluorescence, after removing lumen contents, was greater in Bcrp knockout (KO) mice versus WT mice due to PhA enterocyte absorption and lack of PhA efflux by Bcrp. This difference was eliminated by maintaining the mice on an alfalfa (chlorophyll/PhA)-free diet. The area under the fluorescence ratio-time curve up to 6 hours (AUC_{FL 0-6 h}) of orally administrated PhA was 3.5 times greater in the Bcrp KO mice compared with WT mice, and the PhA serum concentration was 50-fold higher in KO mice. Pretreatment with known BCRP inhibitors lapatinib, curcumin, elacridar, pantoprazole, and sorafenib, at clinically relevant doses, significantly increased PhA AUC_{FL 0-6 h} by 2.4-, 2.3-, 2.2-, 1.5-, and 1.4-fold, respectively, whereas the area under PhA serum concentration-time curve calculated up to 6 hours (AUC_{Serum 0-6 h}) increased by 13.8-, 7.8-, 5.2-, 2.02-, and 1.45-fold, respectively, and corresponded to their hierarchy as in vitro BCRP inhibitors. Our results demonstrate that live animal imaging using PhA can be used to identify BCRP inhibitors and to assess the potential for BCRP-mediated clinical drug-drug interactions.

Therapeutic Potential and Utility of Elacridar with Respect to P-glycoprotein Inhibition: An Insight from the Published In Vitro, Preclinical and Clinical Studies

The occurrence of efflux mechanisms via Permeability-glycoprotein (P-gp) recognized as an important physiological process impedes drug entry or transport across membranes into tissues. In some instances, either low oral bioavailability or lack of brain penetration has been attributed to P-gp mediated efflux activity. Therefore, the objective of development of P-gp inhibitors was to facilitate the attainment of higher drug exposures in tissues. Many third-generation P-gp inhibitors such as elacridar, tariquidar, zosuquidar, etc. have entered clinical development to fulfil the promise. The body of evidence from in vitro and in vivo preclinical and clinical data reviewed in this paper provides the basis for an effective blockade of P-gp efflux mechanism by elacridar. However, clinical translation of the promise has been elusive not just for elacridar but also for other P-gp inhibitors in this class. The review provides introspection and perspectives on the lack of clinical translation of this class of drugs and a broad framework of strategies and considerations in the potential application of elacridar and other P-gp inhibitors in oncology therapeutics.

Ketamine Pharmacokinetics and Pharmacodynamics Are Altered by P-Glycoprotein and Breast Cancer Resistance Protein Efflux Transporters in Mice

To understand the systemic impact of breast cancer resistance protein (Bcrp) and P-glycoprotein (Pgp) deletion, untargeted metabolomics was performed on cerebral spinal fluid (CSF) and plasma of wild-type (WT) and Pgp and Bcrp double-knockout (dKO) rats anesthetized with ketamine-xylazine. We unexpectedly found elevated ketamine levels in both CSF and plasma of dKO versus WT rats. Therefore, the effect of these transporters was investigated on the 1) oral and intraperitoneal serum pharmacokinetics (PK) of ketamine, using a liquid chromatography method (high-performance liquid chromatography with ultraviolet detection), and 2) the anesthetic effect of ketamine using a duration of loss-of-righting reflex (dLORR) test in WT, Bcrp knockout (KO), Pgp KO, and Pgp/Bcrp dKO mice. The PK data demonstrated a significantly increased oral bioavailability and serum exposure of ketamine in dKO > Pgp KO > Bcrp KO mice compared with WT mice. Intraperitoneal ketamine-induced dLORR was significantly longer in dKO > Pgp KO > Bcrp KO > WT mice compared with WT mice. Inhibition of Bcrp and Pgp in WT mice using the dual Pgp/Bcrp inhibitor elacridar increased the ketamine-induced dLORR compared with vehicle-treated mice. The ketamine intracellular concentration was significantly decreased in Madin-Darby canine kidney II BCRP/PGP cells compared with the parental cells. In total, these results demonstrate that ketamine appears to be a dual Pgp/Bcrp substrate whose PK and pharmacodynamics are affected by Pgp and Bcrp-mediated efflux.

A mass spectrometry imaging approach for investigating how drug-drug interactions influence drug blood-brain barrier permeability

There is a high need to develop quantitative imaging methods capable of providing detailed brain localization information of several molecular species simultaneously. In addition, extensive information on the effect of the blood-brain barrier on the penetration, distribution and efficacy of neuroactive compounds is required. Thus, we have developed a mass spectrometry imaging method to visualize and quantify the brain distribution of drugs with varying blood-brain barrier permeability. With this approach, we were able to determine blood-brain barrier transport of different drugs and define the drug distribution in very small brain structures (e.g., choroid plexus) due to the high spatial resolution provided. Simultaneously, we investigated the effect of drug-drug interactions by inhibiting the membrane transporter multidrug resistance 1 protein. We propose that the described approach can serve as a valuable analytical tool during the development of neuroactive drugs, as it can provide physiologically relevant information often neglected by traditional imaging technologies.

Inhibition of ID1-BMPR2 Intrinsic Signaling Sensitizes Glioma Stem Cells to Differentiation Therapy

Purpose: Normal stem cells tightly control self-renewal and differentiation during development, but their neoplastic counterparts, cancer stem cells (CSCs), sustain tumorigenicity both through aberrant activation of stemness and evasion of differentiation. Although regulation of CSC stemness has been extensively studied, the molecular mechanisms suppressing differentiation remain unclear.Experimental Design: We performed in silico screening and in vitro validation studies through Western blotting, qRT-PCR for treatment of WNT and SHH signaling inhibitors, and BMP signaling inducer with control and ID1-overexpressing cells. We also performed in vivo drug treatment assays with Balb/c nude mice.Results: Inhibitor of differentiation 1 (ID1) abrogated differentiation signals from bone morphogenetic protein receptor (BMPR) signaling in glioblastoma stem cells (GSCs) to promote self-renewal. ID1 inhibited BMPR2 expression through miRNAs, miR-17 and miR-20a, which are transcriptional targets of MYC. ID1 increases MYC expression by activating WNT and SHH signaling. Combined pharmacologic blockade of WNT and SHH signaling with BMP treatment significantly suppressed GSC self-renewal and extended survival of tumor-bearing mice.Conclusions: Collectively, our results suggested that ID1 simultaneously regulates stemness through WNT and SHH signaling and differentiation through BMPR-mediated differentiation signaling in GSCs, informing a novel therapeutic strategy of combinatorial targeting of stemness and differentiation. Clin Cancer Res; 24(2); 383-94. ©2017 AACR.

Pyrano[3,2-a]carbazole alkaloids as effective agents against ischemic stroke in vitro and in vivo

A series of pyrano[3,2-a]carbazole alkaloids were designed and synthesized as analogues of Claulansine F (Clau F, 10a) isolated from Clausena lansium. Some of compounds showed strong neuroprotective effects and were promising agents against ischemic stroke. Among these compounds, 7c was the most active in inhibiting the programmed death of PC12 cells and primary cortical neurons. This compound induced neuroprotection following ischemic reperfusion and decreased neurological deficit scores in treated animals. Furthermore, 7c could penetrate the blood-brain barrier (BBB) in rats, and its exposure in the brain was 4.3-fold higher than that in plasma. More importantly, compared to edaravone, 7c exhibited stronger free radical scavenging activity. Our findings suggest that 7c may be promising for further evaluation as an intervention for ischemic stroke.

Pharmaceutical development of an amorphous solid dispersion formulation of elacridar hydrochloride for proof-of-concept clinical studies

OBJECTIVE

A novel tablet formulation containing an amorphous solid dispersion (ASD) of elacridar hydrochloride was developed with the purpose to resolve the drug's low solubility in water and to conduct proof-of-concept clinical studies.

SIGNIFICANCE

Elacridar is highly demanded for proof-of-concept clinical trials that study the drug's suitability to boost brain penetration and bioavailability of numerous anticancer agents. Previously, clinical trials with elacridar were performed with a tablet containing elacridar hydrochloride. However, this tablet formulation resulted in poor and unpredictable absorption which was caused by the low aqueous solubility of elacridar hydrochloride.

METHODS

Twenty four different ASDs were produced and dissolution was compared to crystalline elacridar hydrochloride and a crystalline physical mixture. The formulation with highest dissolution was characterized for amorphicity. Subsequently, a tablet was developed and monitored for chemical/physical stability for 12 months at +15-25 °C, +2-8 °C and -20 °C.

RESULTS

The ASD powder was composed of freeze dried elacridar hydrochloride-povidone K30-sodium dodecyl sulfate (1:6:1, w/w/w), appeared fully amorphous and resulted in complete dissolution whereas crystalline elacridar hydrochloride resulted in only 1% dissolution. The ASD tablets contained 25 mg elacridar hydrochloride and were stable for at least 12 months at -20 °C.

CONCLUSIONS

The ASD tablet was considered feasible for proof-of-concept clinical studies and is now used as such.

TKI combination therapy: strategy to enhance dasatinib uptake by inhibiting Pgp- and BCRP-mediated efflux

The overexpression of efflux transporters, especially P-glycoprotein (Pgp, MDR1, ABCB1) and breast cancer resistance protein (BCRP, ABCG2), represents an important mechanism of multidrug resistance (MDR). Tyrosine kinase inhibitors (TKIs), a novel group of target-specific anticancer drugs, have recently been found to interact with Pgp and BCRP and to serve as both substrates and inhibitors. Considering their dual role, we anticipate that combination TKI therapy may represent a promising strategy to reverse efflux transporter mediated TKI resistance. Presently, investigations on these interactions are very limited. To fill the literature gap, dasatinib was used as the model drug and the effects of various TKIs on Pgp- and BCRP- mediated dasatinib efflux were evaluated. Cell uptake studies were performed using LLC-PK1 and MDCK-II cells along with their subclones that were transfected with human Pgp and BCRP, respectively. Among the 14 TKIs screened, nine TKIs greatly inhibited Pgp-mediated dasatinib efflux at 50 μm. Further concentration dependent studies showed that imatinib, nilotinib and pazopanib were potent Pgp inhibitors with IC₅₀ values of 2.42, 6.11 and 8.06 μm, respectively. Additionally, 50 μm of five TKIs greatly increased dasatinib accumulation through BCRP inhibition. Concentration dependent studies revealed that imatinib, erlotinib, nilotinib, axitinib and pazopanib were potent BCRP inhibitors with IC₅₀ values of 0.94, 2.23, 2.50, 6.89 and 10.4 μm, respectively. Our findings point to potential combinations of TKIs that could enhance intracellular concentrations of the targeted TKI, overcome MDR and improve TKI efficacy. Further in vivo studies are warranted to confirm the efflux transporter-mediated TKI-TKI interaction. Copyright © 2016 John Wiley & Sons, Ltd.

Strategies to Inhibit ABCB1- and ABCG2-Mediated Efflux Transport of Erlotinib at the Blood-Brain Barrier: A PET Study on Nonhuman Primates

The tyrosine kinase inhibitor erlotinib poorly penetrates the blood-brain barrier (BBB) because of efflux transport by P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2), thereby limiting its utility in the treatment of non-small cell lung cancer metastases in the brain. Pharmacologic strategies to inhibit ABCB1/ABCG2-mediated efflux transport at the BBB have been successfully developed in rodents, but it remains unclear whether these can be translated to humans given the pronounced species differences in ABCG2/ABCB1 expression ratios at the BBB. We assessed the efficacy of two different ABCB1/ABCG2 inhibitors to enhance brain distribution of ¹¹C-erlotinib in nonhuman primates as a model of the human BBB.

METHODS

Papio anubis baboons underwent PET scans of the brain after intravenous injection of ¹¹C-erlotinib under baseline conditions (n = 4) and during intravenous infusion of high-dose erlotinib (10 mg/kg/h, n = 4) or elacridar (12 mg/kg/h, n = 3).

RESULTS

Under baseline conditions, ¹¹C-erlotinib distribution to the brain (total volume of distribution [V_T], 0.22 ± 0.015 mL/cm³) was markedly lower than its distribution to muscle tissue surrounding the skull (V_T, 0.86 ± 0.10 mL/cm³). Elacridar infusion resulted in a 3.5 ± 0.9-fold increase in ¹¹C-erlotinib distribution to the brain (V_T, 0.81 ± 0.21 mL/cm³, P < 0.01), reaching levels comparable to those in muscle tissue, without changing ¹¹C-erlotinib plasma pharmacokinetics. During high-dose erlotinib infusion, ¹¹C-erlotinib brain distribution was also significantly (1.7 ± 0.2-fold) increased (V_T, 0.38 ± 0.033 mL/cm³, P < 0.05), with a concomitant increase in ¹¹C-erlotinib plasma exposure.

CONCLUSION

We successfully implemented ABCB1/ABCG2 inhibition protocols in nonhuman primates resulting in pronounced increases in brain distribution of ¹¹C-erlotinib. For patients with brain tumors, such inhibition protocols may ultimately be applied to create more effective treatments using drugs that undergo efflux transport at the BBB.

Validation of a liquid chromatographic method for the pharmaceutical quality control of products containing elacridar

Many anticancer drugs have an impaired bioavailability and poor brain penetration because they are substrates to drug efflux pumps such as P-glycoprotein and Breast Cancer Resistance Protein. Elacridar is a strong inhibitor of these two drug efflux pumps and therefore has great potential to improve oral absorption and brain penetration of many anticancer drugs. Currently, a clinical formulation of elacridar is unavailable and therefore the pharmaceutical development of a drug product is highly warranted. This also necessitates the availability of an analytical method for its quality control. A reverse-phase high-performance liquid chromatographic method with ultraviolet detection was developed for the pharmaceutical quality control of products containing elacridar as the active pharmaceutical ingredient. The analytical method was validated for linearity, accuracy, precision, selectivity, carry-over, stability of stock and reference solutions, stability of the final extract, stability-indicating capability and impurity testing. We found that elacridar is unstable in aqueous solutions that are exposed to light because a hydroxylation product of elacridar is formed. Therefore, sample solutions with elacridar must be protected from light.

ABCG2 and ABCB1 Limit the Efficacy of Dasatinib in a PDGF-B-Driven Brainstem Glioma Model

Dasatinib is a multikinase inhibitor in clinical trials for glioma, and thus far has failed to demonstrate significant efficacy. We investigated whether the ABC efflux transporters ABCG2 and ABCB1 expressed in the blood-brain barrier (BBB), are limiting the efficacy of dasatinib in the treatment of glioma using genetic and pharmacologic approaches. We utilized a genetic brainstem glioma mouse model driven by platelet-derived growth factor-B and p53 loss using abcg2/abcb1 wild-type (ABC WT) or abcg2/abcb1 knockout mice (ABC KO). First, we observed that brainstem glioma tumor latency is significantly prolonged in ABC KO versus ABC WT mice (median survival of 47 vs. 34 days). Dasatinib treatment nearly doubles the survival of brainstem glioma-bearing ABC KO mice (44 vs. 80 days). Elacridar, an ABCG2 and ABCB1 inhibitor, significantly increases the efficacy of dasatinib in brainstem glioma-bearing ABC WT mice (42 vs. 59 days). Pharmacokinetic analysis demonstrates that dasatinib delivery into the normal brain, but not into the tumor core, is significantly increased in ABC KO mice compared with ABC WT mice. Surprisingly, elacridar did not significantly increase dasatinib delivery into the normal brain or the tumor core of ABC WT mice. Next, we demonstrate that the tight junctions of the BBB of this model are compromised as assessed by tissue permeability to Texas Red dextran. Finally, elacridar increases the cytotoxicity of dasatinib independent of ABCG2 and ABCB1 expression in vitro In conclusion, elacridar improves the efficacy of dasatinib in a brainstem glioma model without significantly increasing its delivery to the tumor core. Mol Cancer Ther; 15(5); 819-29. ©2016 AACR.

NKTR-102 Efficacy versus irinotecan in a mouse model of brain metastases of breast cancer

Background

Brain metastases are an increasing problem in women with invasive breast cancer. Strategies designed to treat brain metastases of breast cancer, particularly chemotherapeutics such as irinotecan, demonstrate limited efficacy. Conventional irinotecan distributes poorly to brain metastases; therefore, NKTR-102, a PEGylated irinotecan conjugate should enhance irinotecan and its active metabolite SN38 exposure in brain metastases leading to brain tumor cytotoxicity.

Methods

Female nude mice were intracranially or intracardially implanted with human brain seeking breast cancer cells (MDA-MB-231Br) and dosed with irinotecan or NKTR-102 to determine plasma and tumor pharmacokinetics of irinotecan and SN38. Tumor burden and survival were evaluated in mice treated with vehicle, irinotecan (50 mg/kg), or NKTR-102 low and high doses (10 mg/kg, 50 mg/kg respectively).

Results

NKTR-102 penetrates the blood-tumor barrier and distributes to brain metastases. NKTR-102 increased and prolonged SN38 exposure (>20 ng/g for 168 h) versus conventional irinotecan (>1 ng/g for 4 h). Treatment with NKTR-102 extended survival time (from 35 days to 74 days) and increased overall survival for NKTR-102 low dose (30 % mice) and NKTR-102 high dose (50 % mice). Tumor burden decreased (37 % with 10 mg/kg NKTR-102 and 96 % with 50 mg/kg) and lesion sizes decreased (33 % with 10 mg/kg NKTR-102 and 83 % with 50 mg/kg NKTR-102) compared to conventional irinotecan treated animals.

Conclusions

Elevated and prolonged tumor SN38 exposure after NKTR-102 administration appears responsible for increased survival in this model of breast cancer brain metastasis. Further, SN38 concentrations observed in this study are clinically achieved with 145 mg/m² NKTR-102, such as those used in the BEACON trial, underlining translational relevance of these results.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1672-4) contains supplementary material, which is available to authorized users.

In Vivo Imaging of Human MDR1 Transcription in the Brain and Spine of MDR1-Luciferase Reporter Mice

P-glycoprotein (Pgp) [the product of the MDR1 (ABCB1) gene] at the blood-brain barrier (BBB) limits central nervous system (CNS) entry of many prescribed drugs, contributing to the poor success rate of CNS drug candidates. Modulating Pgp expression could improve drug delivery into the brain; however, assays to predict regulation of human BBB Pgp are lacking. We developed a transgenic mouse model to monitor human MDR1 transcription in the brain and spinal cord in vivo. A reporter construct consisting of ∼10 kb of the human MDR1 promoter controlling the firefly luciferase gene was used to generate a transgenic mouse line (MDR1-luc). Fluorescence in situ hybridization localized the MDR1-luciferase transgene on chromosome 3. Reporter gene expression was monitored with an in vivo imaging system following D-luciferin injection. Basal expression was detectable in the brain, and treatment with activators of the constitutive androstane, pregnane X, and glucocorticoid receptors induced brain and spinal MDR1-luc transcription. Since D-luciferin is a substrate of ABCG2, the feasibility of improving D-luciferin brain accumulation (and luciferase signal) was tested by coadministering the dual ABCB1/ABCG2 inhibitor elacridar. The brain and spine MDR1-luc signal intensity was increased by elacridar treatment, suggesting enhanced D-luciferin brain bioavailability. There was regional heterogeneity in MDR1 transcription (cortex > cerebellum) that coincided with higher mouse Pgp protein expression. We confirmed luciferase expression in brain vessel endothelial cells by ex vivo analysis of tissue luciferase protein expression. We conclude that the MDR1-luc mouse provides a unique in vivo system to visualize MDR1 CNS expression and regulation.

Pharmacokinetics and Brain Distribution and Metabolite Identification of Coptisine, a Protoberberine Alkaloid with Therapeutic Potential for CNS Disorders, in Rats

Coptisine (COP), a protoberberine alkaloid (PBA) from Chinese medicinal plants (such as family Berberidaceae), may be useful for improving central nervous system disorders. However, its pharmacokinetics, disposition and metabolism are not well defined. In the present study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was established for the analysis of COP in biological samples. To better understand its in vivo pharmacological activities, COP concentrations in rat plasma were determined after oral (50 mg/kg) and intravenous administration (10 mg/kg). For the brain distribution study, the concentration of COP in five different regions was examined after intravenous administration at 10 mg/kg. Pharmacokinetic parameters from the COP concentration-time profiles in plasma and brain, and the brain-to-plasma coefficient (Kp, brain) were calculated by non-compartmental analysis. The metabolites of COP in rats in vivo and in vitro (urine, bile, liver microsomes and intestinal bacteria incubation) were also identified. Seventeen metabolites, including 11 unconjugated metabolites formed by hydroxylation, hydrogenation, demethylation, dehydrogenation, demethylation, and 6 glucuronide and sulfate conjugates were identified for the first time. The results suggested that COP had low oral bioavailability of 8.9% and a short (plasma) half-life (T1/2=0.71 h) in rats. After intravenous administration, it quickly crossed the blood-brain barrier, accumulating at higher concentrations and then was slowly eliminated from different brain regions. Moreover, COP was transformed into metabolites through multiple metabolic pathways in vivo and in vitro. These results should help to promote further research on COP and contribute to clarifying the metabolic pathways of PBAs.

Brain Exposure of Two Selective Dual CDK4 and CDK6 Inhibitors and the Antitumor Activity of CDK4 and CDK6 Inhibition in Combination with Temozolomide in an Intracranial Glioblastoma Xenograft

Effective treatments for primary brain tumors and brain metastases represent a major unmet medical need. Targeting the CDK4/CDK6-cyclin D1-Rb-p16/ink4a pathway using a potent CDK4 and CDK6 kinase inhibitor has potential for treating primary central nervous system tumors such as glioblastoma and some peripheral tumors with high incidence of brain metastases. We compared central nervous system exposures of two orally bioavailable CDK4 and CDK6 inhibitors: abemaciclib, which is currently in advanced clinical development, and palbociclib (IBRANCE; Pfizer), which was recently approved by the U.S. Food and Drug Administration. Abemaciclib antitumor activity was assessed in subcutaneous and orthotopic glioma models alone and in combination with standard of care temozolomide (TMZ). Both inhibitors were substrates for xenobiotic efflux transporters P-glycoprotein and breast cancer resistant protein expressed at the blood-brain barrier. Brain Kp,uu values were less than 0.2 after an equimolar intravenous dose indicative of active efflux but were approximately 10-fold greater for abemaciclib than palbociclib. Kp,uu increased 2.8- and 21-fold, respectively, when similarly dosed in P-gp-deficient mice. Abemaciclib had brain area under the curve (0-24 hours) Kp,uu values of 0.03 in mice and 0.11 in rats after a 30 mg/kg p.o. dose. Orally dosed abemaciclib significantly increased survival in a rat orthotopic U87MG xenograft model compared with vehicle-treated animals, and efficacy coincided with a dose-dependent increase in unbound plasma and brain exposures in excess of the CDK4 and CDK6 Ki values. Abemaciclib increased survival time of intracranial U87MG tumor-bearing rats similar to TMZ, and the combination of abemaciclib and TMZ was additive or greater than additive. These data show that abemaciclib crosses the blood-brain barrier and confirm that both CDK4 and CDK6 inhibitors reach unbound brain levels in rodents that are expected to produce enzyme inhibition; however, abemaciclib brain levels are reached more efficiently at presumably lower doses than palbociclib and are potentially on target for a longer period of time.

Brain Penetration and Efficacy of Different Mebendazole Polymorphs in a Mouse Brain Tumor Model

PURPOSE

Mebendazole (MBZ), first used as an antiparasitic drug, shows preclinical efficacy in models of glioblastoma and medulloblastoma. Three different mebendazole polymorphs (A, B, and C) exist, and a detailed assessment of the brain penetration, pharmacokinetics, and antitumor properties of each individual mebendazole polymorph is necessary to improve mebendazole-based brain cancer therapy.

EXPERIMENTAL DESIGN AND RESULTS

In this study, various marketed and custom-formulated mebendazole tablets were analyzed for their polymorph content by IR spectroscopy and subsequently tested in an orthotopic GL261 mouse glioma model for efficacy and tolerability. The pharmacokinetics and brain concentration of mebendazole polymorphs and two main metabolites were analyzed by LC/MS. We found that polymorph B and C both increased survival in a GL261 glioma model, as B exhibited greater toxicity. Polymorph A showed no benefit. Polymorph B and C both reached concentrations in the brain that exceeded the IC₅₀ in GL261 cells 29-fold. In addition, polymorph C demonstrated an AUC₀₋₂₄h brain-to-plasma (B/P) ratio of 0.82, whereas B showed higher plasma AUC and lower B/P ratio. In contrast, polymorph A presented markedly lower levels in the plasma and brain. Furthermore, the combination with elacridar was able to significantly improve the efficacy of polymorph C in GL261 glioma and D425 medulloblastoma models in mice.

CONCLUSIONS

Among mebendazole polymorphs, C reaches therapeutically effective concentrations in the brain tissue and tumor with fewer side effects, and is the better choice for brain cancer therapy. Its efficacy can be further enhanced by combination with elacridar.

Targeting core (mutated) pathways of high-grade gliomas: challenges of intrinsic resistance and drug efflux

High-grade gliomas are the most common type of primary brain tumor and are among the most lethal types of human cancer. Most patients with a high-grade glioma have glioblastoma multiforme (GBM), the most malignant glioma subtype that is associated with a very aggressive disease course and short overall survival. Standard treatment of newly diagnosed GBM involves surgery followed by chemoradiation with temozolomide. However, despite this extensive treatment the mean overall survival is still only 14.6 months and more effective treatments are urgently needed. Although different types of GBMs are indistinguishable by histopathology, novel molecular pathological techniques allow discrimination between the four main GBM subtypes. Targeting the aberrations in the molecular pathways underlying these subtypes is a promising strategy to improve therapy. In this article, we will discuss the potential avenues and pitfalls of molecularly targeted therapies for the treatment of GBM.

Role of P-glycoprotein on the brain penetration and brain pharmacodynamic activity of the MEK inhibitor cobimetinib

Cobimetinib is a MEK inhibitor currently in clinical trials as an anticancer agent. The objectives of this study were to determine in vitro and in vivo if cobimetinib is a substrate of P-glycoprotein (P-gp) and/or breast cancer resistance protein (Bcrp1) and to assess the implications of efflux on cobimetinib pharmacokinetics (PK), brain penetration, and target modulation. Cell lines transfected with P-gp or Bcrp1 established that cobimetinib was a substrate of P-gp but not a substrate of Bcrp1. In vivo, after intravenous and oral administration of cobimetinib to FVB (wild-type; WT), Mdr1a/b(-/-), Bcrp1 (-/-), and Mdr1a/b(-/-)/Bcrp(-/-) knockout (KO) mice, clearance was similar in WT (35.5 ± 16.7 mL/min/kg) and KO animals (22.0 ± 3.6 to 27.6 ± 5.2 mL/min/kg); oral exposure was also similar between WT and KO animals. After an oral 10 mg/kg dose of cobimetinib, the mean total brain to plasma ratio (Kp) at 6 h postdose was 0.3 and 0.2 in WT and Bcrp1(-/-) mice, respectively. In Mdr1a/b(-/-) and Mdr1a/1b/Bcrp1(-/-) KO mice and WT mice treated with elacridar (a P-gp and BCRP inhibitor), Kp increased to 11, 6, and 7, respectively. Increased brain exposure in Mdr1a/b(-/-) and Mdr1a/1b/Bcrp1(-/-) KO and elacridar treated mice was accompanied by up to ∼65% suppression of the target (pErk) in brain tissue, compared to WT mice. By MALDI imaging, the cobimetinib signal intensity was relatively high and was dispersed throughout the brain of Mdr1a/1b/Bcrp1(-/-) KO mice compared to low/undetectable signal intensity in WT mice. The efflux of cobimetinib by P-gp may have implications for the treatment of patients with brain tumors/metastases.

Increased oral availability and brain accumulation of the ALK inhibitor crizotinib by coadministration of the P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) inhibitor elacridar

Crizotinib is an oral tyrosine kinase inhibitor approved for treating patients with non-small cell lung cancer (NSCLC) containing an anaplastic lymphoma kinase (ALK) rearrangement. We used knockout mice to study the roles of P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) in plasma pharmacokinetics and brain accumulation of oral crizotinib, and the feasibility of improving crizotinib kinetics using coadministration of the dual ABCB1/ABCG2 inhibitor elacridar. In vitro, crizotinib was a good transport substrate of human ABCB1, but not of human ABCG2 or murine Abcg2. With low-dose oral crizotinib (5 mg/kg), Abcb1a/1b(-/-) and Abcb1a/1b;Abcg2(-/-) mice had an approximately twofold higher plasma AUC than wild-type mice, and a markedly (~40-fold) higher brain accumulation at 24 hr. Also at 4 hr, crizotinib brain concentrations were ∼25-fold, and brain-to-plasma ratios ~14-fold higher in Abcb1a/1b(-/-) and Abcb1a/1b;Abcg2(-/-) mice than in wild-type mice. High-dose oral crizotinib (50 mg/kg) resulted in comparable plasma pharmacokinetics between wild-type and Abcb1a/1b(-/-) mice, suggesting saturation of intestinal Abcb1. Nonetheless, brain accumulation at 24 hr was still ~70-fold higher in Abcb1a/1b(-/-) than in wild-type mice. Importantly, oral elacridar coadministration increased the plasma and brain concentrations and brain-to-plasma ratios of crizotinib in wild-type mice, equaling the levels in Abcb1a/1b;Abcg2(-/-) mice. Our results indicate that crizotinib oral availability and brain accumulation were primarily restricted by Abcb1 at a non-saturating dose, and that coadministration of elacridar with crizotinib could substantially increase crizotinib oral availability and delivery to the brain. This principle might be used to enhance therapeutic efficacy of crizotinib against brain metastases in NSCLC patients.

Novel hybrids of optically active ring-opened 3-n-butylphthalide derivative and isosorbide as potential anti-ischemic stroke agents

In search of novel anti-ischemic stroke agents with higher potency than a known drug 3-n-butylphthalide (NBP), a series of hybrids ((S)- and (R)-5a-f) from optically active ring-opened NBP derivative and isosorbide were synthesized for evaluating their anti-ischemic stroke activity. Compound (S)-5e displayed the strongest activity in inhibiting the adenosine diphosphate (ADP) and arachidonic acid (AA)-induced platelet aggregation in vitro, with 10.0- and 8.4-fold more effectiveness than (S)-NBP, respectively. Furthermore, (S)-5e was stable in artificial gastrointestinal fluids and could penetrate the blood-brain barrier (BBB) with an appreciate lipid/water partition coefficient relative to (S)-NBP. More importantly, oral treatment with (S)-5e protected from acute thrombosis and inhibited the ischemia/reperfusion-related brain injury in animals. Our findings suggest that (S)-5e may be promising for further evaluation for the intervention of ischemic stroke.

Saturable active efflux by p-glycoprotein and breast cancer resistance protein at the blood-brain barrier leads to nonlinear distribution of elacridar to the central nervous system

The study objective was to investigate factors that affect the central nervous system (CNS) distribution of elacridar. Elacridar inhibits transport mediated by P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) and has been used to study the influence of transporters on brain distribution of chemotherapeutics. Adequate distribution of elacridar across the blood-brain barrier (BBB) and into the brain parenchyma is necessary to target tumor cells in the brain that overexpress transporters and reside behind an intact BBB. We examined the role of P-gp and Bcrp on brain penetration of elacridar using Friend leukemia virus strain B wild-type, Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) mice. Initially, the mice were administered 2.5 mg/kg of elacridar intravenously, and the plasma and brain concentrations were determined. The brain-to-plasma partition coefficient of elacridar in the wild-type mice was 0.82, as compared with 3.5 in Mdr1a/b(-/-) mice, 6.6 in Bcrp1(-/-) mice, and 15 in Mdr1a/b(-/-)Bcrp1(-/-) mice, indicating that both P-gp and Bcrp limit the brain distribution of elacridar. The four genotypes were then administered increasing doses of elacridar, and the CNS distribution of elacridar was determined. The observed and model predicted maximum brain-to-plasma ratios (Emax) at the highest dose were not significantly different in all genotypes. However, the ED50 was lower for Mdr1a/b(-/-) mice compared with Bcrp1(-/-) mice. These findings correlate with the relative expression of P-gp and Bcrp at the BBB in these mice and demonstrate the quantitative enhancement in elacridar CNS distribution as a function of its dose. Overall, this study provides useful concepts for future applications of elacridar as an adjuvant therapy to improve targeting of chemotherapeutic agents to tumor cells in the brain parenchyma.

Development and evaluation of a novel microemulsion formulation of elacridar to improve its bioavailability

The study objective was to develop a formulation of elacridar to overcome its dissolution-rate-limited bioavailability. Elacridar is a P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) inhibitor that has been used to improve the brain distribution of drugs that are substrates of P-gp and BCRP. The chronic use of elacridar is restricted because of the poor solubility leading to poor oral bioavailability. A microemulsion formulation using Cremophor EL, Carbitol, and Captex 355 (6:3:1) was developed. The elacridar microemulsion was effective in the inhibition of P-gp and Bcrp in Madin-Darby canine kidney II-transfected cells. Friend Leukemia Virus Strain B (FVB) mice were used to determine the bioavailability of elacridar after a 10 mg/kg dose of elacridar in the microemulsion, intraperitoneally (i.p.) and orally (p.o.); and the absolute bioavailability was determined to be 1.3 and 0.47, respectively. Coadministration of elacridar microemulsion i.p. with p.o. erlotinib in FVB mice improved the erlotinib brain penetration threefold. The current study shows that a microemulsion formulation of elacridar is effective in improving the bioavailability of elacridar and is an effective inhibitor of P-gp and Bcrp, in vitro and in vivo. It offers an alternative to the suspension and allows a decrease in the dose required to achieve a significant inhibitory effect at the blood-brain barrier.

Strategies for overcoming the blood-brain barrier for the treatment of brain metastases

The era of targeted therapy for cancer has been punctuated by some resounding successes, but with few exceptions, metastases to the brain remain frustratingly difficult to treat. It is increasingly apparent that old concerns regarding the ability of therapeutic agents to penetrate the blood-brain barrier have not been brushed aside by high-affinity small-molecule kinase inhibitors and monoclonal antibodies. Indeed, illustrative trends, such as the increasing incidence of brain metastases from HER2(+) breast cancer since the advent of trastuzumab therapy, have helped to solidify the concept of the CNS as a sanctuary site for cancer. With 200,000 patients diagnosed with brain metastases in the USA each year, the therapeutic challenge posed by the blood-brain barrier continues to be a big problem.

Pharmacokinetics of single ascending doses of the P-glycoprotein inhibitor tariquidar in healthy subjects

We assessed the pharmacokinetics (PK), tolerability and safety of tariquidar (TQD), a P-glycoprotein (Pgp) inhibitor, after intravenous administration of single ascending doses. Employed doses were up to 4-fold higher than in previous clinical trials in cancer patients and are capable of inhibiting Pgp at the blood-brain barrier. Fifteen male healthy volunteers were randomized to receive single intravenous doses of TQD at 4, 6 or 8 mg/kg body weight and underwent blood sampling for over 24 h. TQD concentrations were determined in plasma samples with high-performance liquid chromatography mass spectrometry. No dose-limiting toxicities of TQD were observed. The area under the plasma concentration-time curve from start until 24 h after the end of infusion was positively correlated with an administered TQD dose (r = 0.8981, p < 0.0001). Moreover, we found a positive correlation for volume of distribution at steady state (r = 0.7129, p = 0.0004) with TQD dose. Dose dependency of volume of distribution at steady state points to non-linear PK of TQD, which was in all likelihood caused by transporter saturation at high TQD doses. Acceptable safety and tolerability as well as dose-linear increases in plasma exposure support the future use of TQD at doses up to 8 mg/kg to inhibit Pgp at the human blood-brain barrier.